Diesel 101 Question

[bfrenock]

Speaking specifically about my Boomer 30, when the ignition is turned to the on/run position, the glow plugs are energized for a period by a timer. At the same time, what I assume is the fuel pump is also running as the fuel filter is vibrating in time with it. If the fuel pump is running here, and left in that position for minutes without actually starting the engine, does the pump just keep dumping/pumping fuel into the cylinders?

And after the engine is running, when the key is turned off, I assume the fuel pump stops and that is what kills the engine?

Or is there much more involved?

Thank you for your time. Have a great day!

Bob

 

[the old grind]

:welcome:

It's a bit more 'involved', but not a lot. Traditional diesel injector pumps (now electronic nozzles/computer vs mechanical, if newer 'common rail' injection system) control both the amount and timing of every drop/squirt/atom of fuel. Injector pumps are positive displacement type, and engine speed/power is controlled by length/volume of 'shot'. Governor tweaks/overrides hand-control position to maintain rpm, same as small gas engines.

'Fuel/lift pumps' that supply injector pumps are centrifugal-type like water pumps, will freewheel & run w/less load when output is blocked. (like how your vacuum revs up when plugged & 'unloaded') No big deal with your well either when they're turned off by pressure switch or key.

(btw, My '04 TC33DA doesn't seem to have a glow timer and/or indicator light with key in run position, but they work ok when cranking. My similar '06 and '13 Shibaura-built CUTs have the typical 'glow' position when turning the key. If I find a loose/broken wire or bad ignition switch, I'll share.)

Anyway, when you turn the key to off, a 'normally closed' solenoid inside the injector pump shuts off supply to it. Cylinders burn what spurts out as each is starved into stalling. No amounts are pooling in cylinders or anything that scary, unless you have a leaking injector, not a very common thing. I'm sure you're ok for now, esp if operating symptoms haven't scared the bejeebers out of you. We'll be here if that happens. t o g

 

[bfrenock]

Thanks!

 

[Agvg]

The feeding pump will hold a certain fuel pressure, and all diesels have return to tank so it will just circulate the fuel in the system.

This has nothing to do with the high pressure system that feeds the engine, it just provide fuel for the high pressure pump or pumps if it's a older design. Newer injection systems is around 30000psi or higher so it's pretty hard core.

 

[bfrenock]

Thank you. I now understand how the feeding pump can run more or less indefinitely. So then what controls the high pressure pump. Is that mechanical or electronic? If my engine tends to start in the 'start' key position, but then dies when released into the 'on' position, is that still likely the controller not letting the high pressure pump continue feeding fuel, essentially an electronic error?

Thank you for your time. Have a great day!

Bob

 

[aczlan]

It depends on the tractor, on an older tractor, the high pressure pump is mechanical and there is a electric solenoid to shut off fuel to the pump. When you shut the tractor off that shuts off fuel for 30 seconds or 15 seconds or whatever the manufacturer has set which kills the engine.
In your case, it sounds more like you're key switch is bad and it is not providing the run signal to the engine when it is in run position, only then it is in start position.
I would try flushing your key switch out with something like WD-40 or an electrical contact cleaner and lubricator to see if that helps, otherwise I suspect that you are in for a new keyswitch.

Aaron Z

 

[ovrszd]

Welcome to TBN.

I'll let the NH guys answer your question. May require a more descriptive explanation.

So, I turn my key to "on", then further to "start", engine turns over and fires up, then dies the instant I release the key back to "on"??

 

[bfrenock]

Thank you for the replies. NOW, yes, dies when key released. Earlier (sorry should have mentioned) had a more involved failure (see other post Boomer Start Puzzle). I was just trying to get some basic diesel logic to try to troubleshoot my problem. If I can understand the start/run sequence, much more likely I can pin down something to help me .

Bob

 

[the old grind]

It's more likely that your keyswitch is not keeping the injector pump's shutoff solenoid/valve held energized and open when in the run position.

Usually one wire attached to the rear of the pump to check as suggested above for 12v in start & run key positions, and without having to start up. Cheapest voltmeter or 12v test tool is enough.

The pump proves it's ok by running at all. It might bog & stall if the supply pump failed to feed, not just stop instantly like switching it off.

In a recent thread someone fixed a similar problem by flooding the ignition switch through the keyhole with WD-40 and quickly working it on and off.

Several chimed in about our using that as a once/year lube for any/all locks. You learn it can be more often when driving in Michigan Winters.

 

[bfrenock]

Thank you. Aaron suggested that also. Makes sense, on obvious hole for moisture to get into the dash. Going out right now to try it!

Bob